This invention relates in general to a device and a method for detecting an angular position of a rotating object, and in particular to a device and method for detecting the time at which the rotating object passes a given angular position.
Motor vehicle engines often use sensors to detect the angular position of a crankshaft or a valve position, for example, to control the combustion in a cylinder of the motor vehicle engine with reference to the detected position. The pollutant content in the exhaust gases that result from the combustion process depends on the time of ignition. Accurately detecting the crankshaft or valve position allows the combustion process to occur relatively more efficiently, resulting in less pollutants.
Numerous devices are known that can be used for detecting an angular position. There are generally two types of detection errors that occur in such a device for detecting angular position. These include constant angular errors associated with inaccuracies in the positioning of such a device in the vicinity of the object whose angular position is to be detected, or in the positioning of the components of the device relative to one another. The second type of error are those that vary with time, and may, for example, be caused stochastically, as a function of speed of rotation, or thermally. These errors are the result of a number of different causes. Present-day angular position detection devices include inductive magnetic sensors or Hall sensors that interact with magnets attached to the object to be detected. These sensors produce a sensor output signal that changes constantly with the position of the magnet to be detected. The amplitude of the output signal depends to a relatively strong degree on the distance between the object to be detected and the sensor. Changes in the speed of rotation of the object change both the frequency and the shape of the sensor output signal, so that in general no unequivocal conclusion can be drawn about a definite angular position from the level of the sensor output signal.
Two techniques are known for correcting this problem. The first depends on the use of an automatically regulated amplifier to which the sensor output signal is fed and that produces from this a signal with a fixed amplitude. From this it is then assumed that a certain value of the amplifier-controlled signal always corresponds to the same angular position of the object to be detected. This method has the drawback that the regulation reacts to disturbances or eccentricity of the emitter wheel and introduces additional measurement errors in such situations.
The second known technique depends on detecting each signal peak of the sensor output signal, and determining from them the angular position of the object to be detected. It is assumed that the sensor output signal always reaches its maximum level—even when this value fluctuates—at the same angular position of the object to be detected. The problem arises that the output signals of the known inductive magnetic sensors or Hall sensors are primarily sinusoidal and consequently have very flat signal peaks, which are relatively sensitive to noise and interference.
What is needed is a device and a method for detecting an angular position of a rotating object that make possible relatively precise angular detection without automatic amplification control and without detecting the peaks of the sensor output signal, thereby avoiding the problems of the aforementioned two techniques.